ISO 13347-4:2025

Overview

ISO 13347-4:2025 - "Fans - Determination of fan sound power levels under standardized laboratory conditions - Part 4: Sound intensity method" specifies a reproducible laboratory method to determine fan sound power levels using sound intensity measurements on a measurement surface that encloses the fan. The standard defines acoustical environment requirements, measurement-surface geometry, sampling and averaging procedures, instrumentation verification (including use of a Reference Sound Source, RSS), and reporting of results. It applies to fans defined in ISO 5801 and ISO 13349-1 and is limited to airborne sound emission (it does not measure vibration nor vibration‑sensitivity).

Key topics and technical requirements

• Sound intensity method: Measurement of sound intensity on a closed measurement surface surrounding the fan, with surface averaging to calculate sound power.
• Measurement surface and sampling: Guidance on surface location, grid sampling, number of measurement points and scanning or discrete-point approaches.
• Acoustic environment: Requirements for background noise, nearby reflecting surfaces and reverberation control to ensure valid measurements.
• Instrumentation and verification: Use of calibrated sound intensity probes/microphones, field checks, performance verification and use of a Reference Sound Source (RSS) for validation and adjustments.
• Installation categories: Test setups are designed to represent fan physical orientations in accordance with ISO 5801 and ISO 13350 and defined by ISO 13349-1; the 2025 edition extends methods to cover installation category E.
• Calculations and reporting: Procedures for surface-average levels, reference-source adjustments, calculation of overall and third-octave band sound power levels, uncertainty estimation and minimum reporting content.
• Scope limitations: Applies to airborne emissions only; vibration effects are outside the scope. Practical test size is constrained by available test installations.

Applications and who should use it

ISO 13347-4:2025 is intended for:

• Fan manufacturers conducting R&D and product noise characterization.
• Independent acoustic test laboratories performing standardized sound power tests.
• HVAC and ventilation consultants who need reliable sound power data to predict sound pressure levels in installations.
• Certifying bodies and compliance engineers assessing conformity with acoustic requirements.
• Acoustic researchers comparing noise performance across fan designs.

Use this standard to generate reproducible, comparable sound power data for noise labeling, acoustic modelling, product development and procurement specifications.

Related standards

• ISO 5801 - Fans: performance testing using standardized airways
• ISO 9614-1 / ISO 9614-2 - Sound intensity measurement methods (discrete points / scanning)
• ISO 13347-1 - Fans: general overview of sound power determination
• ISO 13349-1 - Fans: vocabulary and installation categories
• ISO 5136 - In-duct method for sound power of fans
• IEC 1043 - Instruments for measurement of sound intensity

Keywords: ISO 13347-4:2025, fan sound power levels, sound intensity method, acoustic testing, measurement surface, installation categories, airborne sound emission, ISO 5801.